The present invention relates to an overlock sewing machine, and more particularly to a two-needle overlock sewing machine capable of sewing a thread chain into a seam.
An overlock sewing machine of this kind was proposed, for example, in Japanese Patent Publication No. 2-30277, in which a middle tongue is projected into a needle hole or drawn back into a needle hole by using a manual operation mechanism. An outer tongue is formed in the cloth feed direction as part of a throat plate, and the middle tongue is parallel to the outer tongue, and is slidably mounted on the throat plate. Before the throat plate, a thread chain holder is disposed, and the thread chain holder is designed to cut off and hold the thread chain. The outer tongue forms part of an opening needle hole.
In this kind of sewing machine, in the sewing process, while the middle tongue is supporting the cloth on the needle hole, a stitch is formed while enveloping the outer tongue and middle tongue. When the end of the cloth passes through the middle tongue and outer tongue, the thread chain is formed on the middle tongue and outer tongue. After the sewing process, a presser foot is raised by manipulation of a push-up lever, and then the middle tongue is drawn backward from the needle hole by manipulation of the manual operation mechanism to pull out the middle tongue from the thread chain. Afterwards, the sewn cloth is pulled out to the cloth feed-out side, and the thread chain consecutive to the cloth is pulled out from the outer tongue. The cloth is then turned to the front side and pulled up, and the thread chain consecutive to the cloth end is inserted into the thread chain holder, and thereby the thread chain is cut off and held at the same time.
In handling the thread chain, as mentioned above, the middle tongue must be drawn back from the needle hole by manipulation of the manual operation mechanism. Since the manual operation mechanism must be manipulated, the cloth could not be handled continuously by both hands. Besides, a control device is needed to move back and forth the middle tongue at a proper timing by using a solenoid or the like, the structure is complicated and the cost is increased.
It is hence an object of the invention to present a two-needle overlock sewing machine capable of simplifying the mechanism for moving back and forth the middle tongue and processing the thread chain after sewing without sacrificing the handling performance of the cloth.
The two-needle overlock sewing machine of the present invention comprises a throat plate, a thread chain holder, a presser foot, spring means, a push-up lever, and a middle tongue. The throat plate includes an opening needle hole, and an outer tongue projecting in the cloth feed direction to compose one side of the needle hole. The thread chain holder is disposed before the throat plate, and is designed to cut off and hold the thread chain. The presser foot is disposed above the throat plate, and the spring means presses the presser foot to the throat plate. The push-up lever lifts up the presser foot from than the throat plate against the action of the spring means. The middle tongue is fitted to the throat plate so as to be movable back and forth in the cloth feed direction. The middle tongue is coupled with the push-up lever by way of a transmission mechanism, and is designed to project into the needle hole in forward motion, and be drawn back from the needle hole in backward motion. That is, when the presser foot is raised by manipulating the push-up lever, the middle tongue is drawn back to retreat from the needle hole.
According to the present invention, after sewing operation, when the presser foot is raised by manipulating the push-up lever, the middle tongue simultaneously retreats from the needle hole, and is pulled out from the thread chain consecutive to the cloth end. It hence omits the manipulation for moving back the middle tongue after raising the presser foot. Therefore, the cloth can be handled by both hands, and the cloth handling performance is enhanced. The transmission mechanism for coupling the push-up lever and middle tongue is only required to have a function of transmitting the motion of the push-up lever to the middle tongue, and does not require solenoid or control device needed when manipulating the middle tongue independently. As a result, the structure is simplified and the cost is lowered.
Preferably, the transmission mechanism is composed of a link mechanism coupled to the middle tongue, a bell crank lever having an intermediate part, for example, rotatably supported on a sewing machine frame, and wire means for coupling the link mechanism and push-up lever. By using the wire means in the transmission mechanism, the structure becomes simpler and the cost is further reduced.
More preferably, the middle tongue is forced in a forward moving direction by the spring, and the wire means and the push-up lever are coupled by the link. The link and push-up lever are coupled together as a slot is formed at either side and a stepped screw is driven in the other through the slot.
In the present invention, by manipulating the push-up lever and raising the presser foot against the action of the spring means, the middle tongue begins to move backward on the way. That is, by manipulating the push-up lever, the stepped screw moves within the slot. When the push-up lever is further manipulated until the stepped screw reaches the end of the slot, the wire means is pulled thereafter, and the middle tongue moves back against the action of the spring, and retreats from the needle hole. Therefore, according to the present invention, while sewing a cloth having a stepped portion, if the presser foot rides over the stepped portion and climbs somewhat, the middle tongue continues to support the cloth in the sewing process in the needle hole without drawing back.
Further preferably, the presser foot and push-up lever compose part of a pressing mechanism, and the pressing mechanism comprises a pivot shaft turnably supported on a sewing machine frame, a presser base elevating in conjunction with the turn of the pivot shaft, with the presser foot fitted at its leading end, and a lever supported rotatably about the pivot shaft for rotating about the pivot shaft in conjunction with the push-up lever, and a rigger part of the pivot shaft and a latch part of the lever are engaged with each other so as to be able to depart in the rotating direction.
In the present invention, similarly, when the presser foot rides over the stepped portion of the cloth, the rigger part of the pivot shaft and the latch part of the lever depart from each other, so that the middle tongue maintains a state projecting into the needle hole.
Other objects and features of the present invention will be more clearly understood from the following explanation about an embodiment taken in conjunction with the accompanying drawings.